This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
There's a syntax error in your second example, so that one's wrong.
To answer your real question, I would always use single quotes when writing SQL queries as not all RDBMS support double quotes. I'm not sure what the ANSI standard says about it.
From a JDBC perspective I'm not sure if it matters as I believe the query string will be processed by the JDBC Driver implementation before being passed on the database in a compatible format. I suppose the degree of processing that takes place would depend on the driver.